The present invention relates to a liquid crystal display apparatus and, more particularly, to an active matrix liquid crystal display apparatus.
In the conventional liquid crystal display apparatus, the electrodes for driving the liquid crystal layer, the electrodes are formed on the surface of two substrates, and transparent electrodes are used, each electrode facing the other. This is because what is used is a display method represented by a Twisted Nematic display method in which the liquid crystal layer is driven by applying an electric field in a transverse direction with respect to the surface of the substrate. On the other hand, for the display method in which an electric field is applied in the direction almost parallel to the surface of the substrate, a display method using comb-type electrodes is disclosed in the Japanese Patent No. 63-21907 (1988) and in U.S. Pat. No. 4,345,249. In this case, the electrodes are not necessarily selected to be transparent, but non-transparent and metallic electrodes with higher electrical conductivity are used. However, in the above description of conventional systems, for both the display method in which the electric field is applied in a direction with respect to the surface of the electrode, (which is designated an "In-plane switching method"), specifically used in the active matrix drive mode, and the horizontal electric field method with low voltage drive, the enabling material property of the liquid crystal layer and the device structure are not described in detail.
In the horizontal electric field method, it is required to make the electrode gap wider in order to attain a higher cross-section for the open port, which raises a problem that the necessary drive voltage becomes higher. In addition, in order to allow the use of a mouse as a pointing device in the liquid crystal display apparatus, it is required to establish a response time between 150 ms and 200 ms, and for enabling a motion picture resolution, the response time is required to be 50 ms. However, since the response of a liquid crystal to an electric field change is inherently slow, it often creates the problem that the response time of the liquid crystal is slow in various kinds of display methods using a Nematic Liquid Crystal. This is not exceptional in the horizontal electric field method. In addition, due to the electrode structure specific to the horizontal electric field method, the electric field will tend not to be fully applied to the liquid crystal, which results in a slower response of the liquid crystal. Thus, some means is required in order to reduce the drive voltage, to enable use of a mouse and to provide an improved motion picture resolution.